1. Field of the Invention
The present invention relates to an apparatus and method for Spatial Division Duplex (SDD) for a millimeter wave communication system. More particularly, the present invention relates to an apparatus and method for a SDD communication system utilizing millimeter electromagnetic waves for peer-to-peer (P2P) wireless communication.
2. Description of the Related Art
Mobile communication has continued to advance in recent years, with the number of subscribers to mobile communication services now exceeding 4.5 billion and continuing to grow. At the same time, new mobile communication technologies and systems have been developed to satisfy increasing needs and to provide more and better mobile communication applications and services to mobile communication users. Examples of such systems include Code Division Multiple Access 2000 (CDMA2000) Evolution Data Optimized (EvDO) systems developed by the 3rd Generation Partnership Project 2 (3GPP2), and Wideband CDMA (WCDMA), High Speed Packet Access (HSPA), and Long Term Evolution (LTE) systems developed by the 3rd Generation Partnership Project (3GPP), and mobile Worldwide Interoperability for Microwave Access (WiMAX) systems developed by the Institute of Electrical and Electronics Engineers (IEEE). As more and more people become users of mobile communication systems, and more data-rich services are provided over these systems, there is an increasing need of a mobile communication system with larger capacity, higher throughput, lower latency, and better reliability.
Millimeter waves are radio waves, with a radio frequency range of 30 GHz-300 GHz, that exhibit unique propagation characteristics due to their smaller wavelengths. For example, more antennas can be packed in a relatively small area, thus enabling a high-gain antenna in small form factor. Millimeter wave wireless communication systems have achieved 10 Gbps data transfer rates over distances of several kilometers. However, the current technologies are not well suited for commercial mobile communication due to issues such as cost, complexity, power consumption, and form factor. Recently, research efforts have been made to utilize the millimeter wave wireless communication systems for short-range wireless communication. For example, progresses in developing 60 GHz Radio Frequency Integrated Circuits (RFIC) and antenna solutions has been achieved, however the 60 GHz RFIC today still suffers from low efficiency and high cost and millimeter waves suffer from propagation loss.
In order to address the propagation loss of millimeter waves, beamforming can be employed. Beamforming is a signal processing technique used for directional signal transmission or reception using special selectivity through adaptive receive/transmit beam patterns in order to achieve a signal gain. When transmitting, a beamformer controls a phase and relative amplitude of a signal at each transmitter antenna in order to create a pattern of constructive and destructive interference in a wavefront. When receiving, information from different antennas is combined so that an expected pattern of radiation is preferentially observed.
FIG. 1 illustrates transmit beam forming according to the related art.
Referring to FIG. 1, a transmitter 100, having multiple transmit antennas 102 in a transmit antenna array 101, is shown.
A transmit beamforming weight, gti, which is shown in FIG. 1 as gain gt1 to gtN, is applied to the signal transmitted from an ith one of the transmit antennas 102 of the antenna array 101. The gain is used to adjust a phase and relative amplitude of the signal transmitted from each of the transmit antennas 102. The signal can be amplified separately for transmission from each of the transmit antennas 102. Alternatively, a single amplifier or amplifiers numbering less than the number of transmit antennas can be used. Moreover, the beamforming weights or gains can be applied before signal amplification or after signal amplification.
FIG. 2 illustrates receive beam forming according to the related art.
Referring to FIG. 2, a receiver 200, having multiple receive antennas 202 in a receive antenna array 201, is shown.
The signal received by each of the receive antennas 202 is amplified by a Low-Noise Amplifier (LNA). A receive beamforming weight, gri, which is shown in FIG. 2 as gr1 to grN, is applied to the signal received and amplified from the ith one of the receive antennas 202. The gain is used to adjust a phase and relative amplitude of the signal received by each of the receive antennas 202. The receive beamforming weight may be a gain adjustment. The phase and amplitude adjusted signals are combined to produce the received signal. The receive beamforming gain is obtained because of coherent or constructive combining of the signals from each of the receive antennas 202.
FIG. 3 illustrates dynamic beamforming according to the related art.
Referring to FIG. 3, a plurality of weights gt1 to gt5 are applied to outgoing signal s(t) to form the equiphase wavefront of a transmit beam TxB.
The weights gt1 to gt5 are only used to control and/or adjust a phase of the signal s(t). The signal s(t) is applied to a plurality of antennas A1 to A5, with each antenna having a corresponding one of the weights gt1 to gt5, and each of the antennas A1 to A5 being spaced apart from adjacent ones of the antennas A1 to A5 by a distance d. For example, as shown in FIG. 3, the signal s(t) is applied to antenna A1, having the weight gt1 of e+j(2μ/λ)2d cos θ which is applied to signals transmitted through the antenna A1, in order to steer the signal s(t) with respect to its phase. The weights gt2 to gt5 are respectively applied to the signal s(t) at the antennas A2 to A5. Thus, each of the antennas A1 to A5 produces a phase adjust signal s(t) that may be steered in a particular direction having the equiphase wavefront shown in FIG. 3. The phase adjustment applied to the antennas A1 to A5 using the weights gt1 to gt5 may be applied to both a transmitting and a receiving of the signal s(t) so that a transmit beam and a receive beam may be steered in a predetermined direction.
FIG. 4 illustrates an example of digital beamforming according to the related art.
Referring to FIG. 4, digital beamforming may be used to achieve various benefits, such as performance and flexibility, as performed by a transceiver 400. As shown in FIG. 4, M, N number of signals, including signals s0(t) to s(M-1)t, are transmitted along respective transmission paths to be transmitted by respective antennas of the transceiver 400. Transmit weights wt0 to wt(M-1) are respectively applied to the signals s0(t) to s(M-1)t along the respective transmission paths, each including a respective Digital to Analog Converter (DAC) DAC1 to DACM. The transmitted signals s0(t) to s(M-1)t are received by respective ones of antennas of the receiver 200. Received signals r0(t) to r(N-1)t are received through respective reception paths, each having a Low Noise Amplifier (LNA) and an Analog to Digital Converter (ADC) ADC1 to ADCN. Receive weights wr0 to wr(N-1) are respectively applied to the received signals r0(t) to r(N-1)t. Thus, by applying digital beamforming to digital signals, optimal channel capacity may be achieved, even under variable channel conditions. However, a large amount of hardware is used in digital beamforming by having M or N full transceivers. Thus, digital beamforming improves channel capacity while increasing both hardware complexity and power consumption.
FIG. 5 illustrates an example of analog beamforming according to the related art.
Referring to FIG. 5, analog beamforming is performed by a transceiver 500. According to the analog beamforming of FIG. 5, a number of data converters, such as the DACs and the ADCs shown in FIG. 4, can be reduced. As shown in FIG. 5, in the transceiver 500, a transmit signal s(t) passes through a DAC 501 to convert a digital form of the transmit signal s(t) into an analog form of the transmit signal s(t), which is then provided to a plurality of transmit antennas 503 along corresponding signal paths. Respective transmit weights wt0 to wt(M-1) are applied to the respective analog signal s(t) passing through the corresponding signal paths, each having a mixer, to the transmit antennas. The transceiver 500 receives the respective analog signals s(t) having the respective transmit weights wt0 to wt(M-1) using a plurality of receive antennas 504. A plurality of received signals pass through respective signal paths, each having an LNA, a mixer, and respective receive weights wr0 to wr(N-1) are applied to the plurality of received signals. The weighted received signals are then converted into a digital signal by an ADC 502 to form a receive signal r(t). Accordingly, in the analog beamforming of FIG. 5 only one DAC 501 and one ADC 502 is used in the transceiver 500, thus reducing a number of data converters.
FIG. 6 illustrates an example of Radio Frequency (RF) beamforming according to the related art.
Referring to FIG. 6, RF beamforming is performed by a transceiver 600. As shown in FIG. 6, RF beamforming may reduce a number of mixers used to perform the beamforming operations. In the transceiver 600, a transmit signal s(t) is converted from a digital form into an analog form using the DAC 601. The analog form of the transmit signal s(t) is then passed through a mixer 602 in order to be provided to a plurality of transmit antennas 603 along respective signal paths in order to be transmitted. The transceiver 600 receives the transmitted signals using a plurality of receive antennas 604, each having a respective signal path including an LNA and respective receive weights wr0 to wr(N-1) applied to the plurality of received signals. The weighted received signals are combined by combiner 605 and then mixed by mixer 606 and passed through an ADC 607 to form the received signal r(t). Thus, a mixer is not disposed along each of the signal paths of the receive antennas 604, and a lower number of mixers results in decreased hardware complexity and power consumption. However, a reduced flexibility in beamforming control, decreased multiple access functionality and decreased multiple access users result in limited functionality of RF beamforming.
Current peer-to-peer (P2P) millimeter wave standards, such as WirelessHD technology, ECMA-387, and IEEE 802.15.3c employ Time Division Duplex (TDD), wherein only one of the two devices in communication transmits or receives at a given time. TDD or Frequency Division Duplex (FDD) are often used to separate the transmitted signals and received signals of base stations in conventional cellular or mobile broadband systems. In conventional TDD systems, base stations transmit in downlink time slots and mobile stations transmit in the uplink time slots. Consequently, current millimeter wave standards only support half-duplex communications. In other words, simultaneous transmit and receive operations are not possible in current P2P millimeter wave standards for wireless communication.